This invention relates to systems and devices for removing foreign matter such as dust from the printing surfaces of plate cylinders of printing presses. More particularly, the invention relates to a system for automatically removing foreign matter such an ink refuse and paper dust (hereinafter referred to collectively as "dust") which has adhered to plate printing surfaces in a printing press during offset printing.
During offset printing, dust adheres to the plate cylinder surfaces and causes white unprinted parts (sometimes called "hickies") resembling pinholes or pimples to be left on the printed material. Heretofore, it has been a common practice for the operator, upon detecting such defects on a proof, to stop the printing press and manually remove the dust. Alternatively, although this is a very dangerous procedure, the operator removes the dust on the rotating plate cylinder surface by means of a rodlike dust removing tool having a tip made of a material such as a rubber material. These dust reremoving procedures, however, respectively give rise to a drop in printing rate and danger to the operator. Accordingly, partially automated systems and devices for dust removal have been proposed.
In one such proposed system, when the operator discovers an unprinted part or hicky on a proof of printer material, he specifically determines the position of the defect relative to a number previously designated in the width direction of the plate cylinder and presses a button at a corresponding position of a control panel thereby to cause a dust removing device installed in confronting relation to the plate cylinder surface to operate. This dust removing device comprises a dust removing head mechanism having at its tip a blade-shaped elastic member, which is caused to contact and wipe the plate cylinder surface during operation, and a shifting mechanism for causing the head mechanism to move to the specified position of the plate cylinder surface. This system, however, has not as yet been reduced to practice because it has the shortcomings described below.
The method of specifying the position of that part of the plate cylinder surface from which dust is to be removed is inaccurate, whereby the dust cannot be positively removed. As described above, the operator determines, by examining the printed proof, the position of the part to be cleaned of dust in correspondence with a number in the width direction of the plate cylinder surface and thereafter pushes what he judges as the appropriate button on the control panel. However, in the case where the unprinted portion is at the central part of the printed material, there is a possibility of an error in the button pressing procedure since the operator judges the button position by eye.
In order to solve this problem, a dust removing device in which the dust removing head mechanism is adapted to carry out scrubbing action has been proposed, but this innovation entails a loss in dust removal time and has not become a practical solution.
The blade-shaped elastic member of the head mechanism also presents a problem. Since it directly contacts and wipes the plate cylinder surface, ink and other matter adhere to the tip part thereof. As a consequence of a number of dust removing operations, the ink accumulated on the blade tip adheres in reverse to the plate cylinder surface and contaminates it. If this ink is left as it is for a number of hours, it will solidify and give rise to trouble such as damage to the plate cylinder and related parts. Accordingly it is necessary for the operator to promptly clean off this ink. This cleaning work is a troublesome burden on the operator.
For this reason, a device for spraying a cleaning agent through a spray nozzle against the blade tip part thereby to automatically clean the same when the dust removing device is in its idle, standby state has been proposed. However, even with this device, it is difficult to achieve thorough cleaning, whereby it has not yet become a practical solution to the problem.